1. Field of the Invention
The present invention relates to an ink jet recording head and the recording by an ink jet recording apparatus. More particularly, the invention relates to the ink jet recording head which uses ink having different densities for the same color series for recording images.
2. Related Background Art
With the wide use of an information processing apparatus, such as a copying machine, a word processor, a computer, and also, of communication equipment, an apparatus which digitally records images by use of a recording head of an ink jet method has rapidly become popular as one of the image formation apparatuses (hereinafter referred to as recording apparatus) serving as information output means for these equipment. For a recording apparatus of the kind, it is generally practiced that the so-called multinozzle head, in which a plurality of ink discharge ports, liquid passages conductively connected to these ports, and others are integrated, is used as a recording element in order to improve the recording speed.
As a recording method of the kind, there is adopted for controlling a recording in an intermediate tone, a dot density control method with which to produce such an intermediate tone by controlling the number of recording dots per unit area by the application of the recording dots of a specific size, or a dot diameter control method with which to produce such an intermediate tone by controlling the sizes of the recording dots.
Here, the latter method which controls the dot diameters requires a complicated control to be carried out for the fine modification of the sizes of the recording dots, hence automatically restrict its implementation. In general, therefore, the former method which controls the dot densities is adopted.
The electro-thermal energy transducing elements, which make a high resolution possible, are used because of the ease with which to prepare the elements in a high density, but it is also difficult to control the amount of pressure variation, thus disabling the diameters of the recording dots to be modulated. For recording, therefore, the method for controlling dot density is adopted.
As one of the typical binarization methods for the intermediate tonal representation used for the dot density control method, an organizational design method may be employed. This method, however, has a problem that the number of gradations is limited by the matrix size. In other words, to increase the number of gradations, it is necessary to make the matrix size larger. If the matrix size is made larger, there is a problem encountered, among others, that one pixel of a recorded image consisting of one matrix becomes greater, thus spoiling the resolution. Also, there is a design method of a conditionally determining type, such as an error diffusion method as another typical type of binarization method. Whereas the aforesaid organizational design method is of an independently determining type for binarization using a threshold value which is not related to any input pixels, this type of method varies the threshold value in consideration of the surrounding pixels of an inputted pixel. The design method of a conditionally determining type which is represented by the error diffusion method has an excellent compatibility of tonality and resolution. Also, when an original image is a printed image, the creation of the moire pattern on the recording image is extremely small among other advantages, but, on the other hand, the graininess of the bright part of the image tends to become conspicuous, and a problem is encountered that the evaluation of the image quality is lowered. This problem is particularly conspicuous in a recording apparatus having a low recording density.
Therefore, in order to make the above-mentioned graininess less conspicuous, there is proposed a method for a conventional ink jet recording apparatus that the two recording heads, which discharge ink having a low density of a recorded image, and ink having a high density thereof, respectively, are provided so that the recording dots are formed with ink having a low density (light ink) for the bright part to the intermediate tonal part of an image, and also formed with ink having a high density (dark ink) for the intermediate tonal part to the dark part of the image.
FIG. 1 is a perspective view showing the principal part of a conventional color ink jet recording apparatus of a serial printing type which uses dark and light ink according to the above-mentioned recording method.
On a carriage 241, there are respectively arranged at a given distance, a recording head Kk which discharges black dark ink; a recording head Ku, black light ink; a recording head Ck which discharges cyan dark ink; a recording head Cu, cyan light ink; a recording head Mk which discharges magenta dark ink; a recording head Mu, magenta light ink; and a recording head Yk which discharges dark yellow ink; a recording head Yu, yellow light ink. The carriage 241 is slidably supported by a guide shaft 243 to be guided to reciprocate along the above-mentioned guide shaft 243 by the driving force of a carriage motor 245 transmitted through a driving belt 244.
In the liquid passages each conductively connected to the respective ink discharge port of each recording head, the heat generating elements (electro-thermal transducers) are arranged to generate the thermal energy used for discharging ink.
The ink used by each of the recording heads is retained in each of the ink cartridges 248 provided for the respective colors, and is supplied through each of the ink supply passages. Also, the control signals and driving signals are transmitted from an apparatus controller to the recording heads through a flexible cable 249.
A recording material such a recording sheet or a plastic thin sheet is conveyed in the direction indicated by arrows in FIG. 1 by means of a feed roller (not shown) and exhaust sheet rollers 242 when a feed motor (not shown) is driven. During this period, a recording is being executed on the surface of the recording material facing the recording heads along the traveling of each of the heads. In other words, in accordance with the reading timing of an encoder (not shown) which detects the traveling positions of the carriage 241, the above-mentioned heat generating elements are driven on the basis of the recording signals to discharge each of the ink, black dark and light, cyan dark and light, magenta dark and light, and yellow dark and light, on the recording material in that order, thus enabling them to adhere thereto for recording images on the material.
In the home position defined outside the recording area in the carriage 241 travels, a recovery unit 246 is arranged with a capping unit 247. With the recovery process by this recovery unit, the ink discharge characteristics are stabilized for each of the recording heads.
The conventional ink jet recording apparatus which uses the dark and light ink as described with reference to FIG. 1 can solve the problem of the graininess of the recorded image comparatively well, and presents one of effective techniques in improving the quality of recorded image. However, there are roughly three problems still to be solved as described below.
1) Firstly, the conventional ink jet recording apparatus which uses the dark and light ink is at first provided with a recording head and an ink cartridge per ink to be used. Consequently, the number of recording heads and ink cartridges is increased, inevitably bringing about a larger size of the apparatus.
Also, the weight of the recording heads and the carriage is increased. At the same time, the distance required for the ramp up and down becomes long when the carriage travels, thus resulting likewise in the larger size of the apparatus. Also, due to.the increased weight, the load required to drive the carriage is increased, necessitating the provision of a driving motor having a greater torque. There is also a need for a complicated mechanism to maintain the capping performance of many numbers of the caps arranged in response to the number of the recording heads, hence increasing the cost accordingly.
Further, as the number of recording heads is increased, it is necessary to register the recording head for each color in a severer precision. Thus expensive parts having a higher precision must be used. Also, the adjustment of complicated positioning and the correction control must be effectuated.
In addition, if the difference between the dot densities is great for the dark and light ink when a recording is made by use of the dark and light ink, the reproduction of the gradation is not linear in the part where the light ink and the dark ink are switched over in a recorded image, and a false contour tends to appear. Also, a problem is encountered that the variations of the graininess and tonality take place in the above-mentioned part where the ink is switched over in the recorded image, thus creating an unnatural image after all. In order to solve this particular problem, a method is adopted to provide more degrees of the densities by use of a low density ink, medium density ink, and high density ink, among others, but it is clear that this method will just promote the above-mentioned problems concerning the size of the apparatus.
2) Secondly, when ink of different densities is used for each of the plural color ink for recording in color, there is a problem that it is not easy to eliminate the unevenness and others in a recorded image due to the order in which each of color ink is superposed, and the order in which each of the same color ink but of different densities is superposed, respectively.
As a conventional technique to eliminate the above-mentioned unevenness and others, it is known that the same technique as to eliminate the uneven densities is applied. This will be described as follows:
In a color printer, for example, it is necessary for recording images to take into account various conditions, such as coloring ability, tonality, uniformity unlike a character printer and others which record only characters. Particularly, as to the uniformity, just a slight variation per nozzle created in the process of fabricating a multinozzle head produces adverse effects on the amount of discharged ink and the direction of discharges per discharge port in recording, resulting in the density unevenness in a recorded image to cause its quality to be degraded.
In conjunction with FIGS. 2A to 3C, the specific examples will be described.
In FIG. 2A, a reference numeral 91 designates the so-called multinozzle head. For simplification, the head is assumed to be structured with eight discharge ports 92 to discharge only one kind of ink having a single color and a single density. A reference numeral 93 designates ink droplets discharged from each of the discharge ports 92. As shown in FIG. 2A, it is ideal that the ink droplets 93 are discharged in the same amount and direction. Then, if the discharges are executed like this, the dots of the same size are recorded on a recording sheet as shown in FIG. 2B, thus making it possible to obtain an over all image uniformly without any density unevenness (see FIG. 2C).
In practice, however, there is often unevenness per discharge port as described earlier, and as shown in FIG. 3A, the amount and direction of ink droplets discharged from each discharge port are varied. Thus, as shown in FIG. 3B, the sizes of the recorded dots become uneven and its impacted positions vary. As a result, there exists a blank part in which the area factor is not satisfied 100% along the main scan direction of the recording head or on the contrary, the dots are superposed more than necessary, or as shown in the central part of FIG. 3B, a white streak is created. In this case, the density distribution is as shown in FIG. 3C. This condition is recognized as a density unevenness after all as far as observed by usual human eyes.
3) Thirdly, when the amount of sheet feeding which is repeated per recording scan is not controlled constantly, it also results in the same kind of density unevenness and others. For example, if the sheet is fed more than a specific amount, the dots in each of the end portions of the scanning area are recorded in the positions which are further apart than a regulated distance. This portion becomes conspicuous as a white streak. On the contrary, if the sheet is fed less than a specific amount, the dots in each of the end portions are superposed more than necessary to make such a portion conspicuous as a black streak. The higher the pixel density, the severer control is needed for the amount of this sheet feeding. If this is not satisfactorily controlled, it is inevitable that joining streaks are created on a recorded image.
In order to prevent the above-mentioned density unevennesses and streaks from being created, the following proposal has been made:
With reference to FIGS. 4A to 5C, such proposed method will be described. As shown in FIGS. 4A to 5C, it is necessary to scan the recording head 91 three times according to this method for the completion of a recording in an area shown in FIGS. 2A to 3C. However, in a half of such an area, that is, an area equivalent to a half of the discharge port region of the recording head, can be completely recorded by scanning the recording head two times. In other words, in this case, the eight discharge ports of the recording head are divided into two groups each four upper discharge ports and four lower discharge ports. For the first scan, the lower four discharge ports are used to record the dots of four pixel arrays, respectively, and then, after feeding the sheet for a portion of four discharge ports, the dots are recorded by the second scan by use of the upper four discharge ports on the portion where no dots of the above-mentioned four pixel arrays are recorded. At this juncture, in each of the second time scans, the dots which should be recorded by the second scan are thinned by approximately a half. Thus the dots to be recorded by each scan are in a complementary relationship. Hereinafter, a recording method such as this is called xe2x80x9cdivided recording methodxe2x80x9d.
With a divided recording method, a recorded image is as shown in FIG. 4B because even when using a recording head whose discharge characteristics vary per discharge port as shown in FIGS. 3A to 3C, its unfavorable effect to the recorded image per discharge port is, reduced by half, hence making the black streak and white streak as shown in FIG. 3B less conspicuous. Therefore, compared to the density unevenness shown in FIG. 3C, there is also a considerable improvement in it as shown in FIG. 4C. Also, the joint streaks appearing at the boundaries between each of the scanning areas can be reduced by half if the divided recording method is applied because the dots on one pixel array are recorded by the discharge ports on the end portion of the recording head and those on the central portion of it.
When such a recording is executed, the image data are divided so that the dots are offset with each other (complementally) in accordance with certain arrays in the first and second scans. Usually, however, this division of the image data (hereinafter, may also be referred to as xe2x80x9cthinned patternsxe2x80x9d) is most often such as shown in FIGS. 5A to 5C so that the dots can be arranged in a cross pattern per pixel vertically and horizontally. Therefore, in a unit recording area (here, a unit of four pixels), a recording is completed by the first scan which records the cross pattern and the second scan which records the counter-cross pattern.
FIGS. 5A, 5B, and 5C are views illustrating the process in which a recording in a specific area is completed by use of the cross and counter-cross patterns, respectively. At first, in the first scan, the dots 51 are recorded to form the cross pattern by use of the lower four nozzles (FIG. 5A). Then, in the second scan, the dots 52 are recorded to from the counter-cross pattern (FIG. 5B) after the sheet is fed for a portion of four pixels (a xc2xd of the head length). Further, in the third scan, the dots 53 are recording to from the cross pattern again (FIG. 5C) after the sheet is again fed for a portion of four pixels (a xc2xd of the head length). In this order, the sheet is fed for a four-pixel unit, and the cross and counter-cross patterns are recorded alternately, thus completing the recording area of the four-pixel unit per scan. As described above, it becomes possible to obtain an image of a high quality, in which the density unevenness is reduced by averaging the effect of the varied discharge characteristics of each discharge port in such a manner that the dots in the same pixel array are being recorded by two different kinds of discharge ports.
A recording method of the kind is disclosed in Japanese Patent Laid-Open Application No. 60-107975 and U.S. Pat. No. 4,967,203, for example, and it is described in these patent specifications, respectively, that the method is effectively applicable to solving the problem of the density unevenness and joint streaks. In the former, it is disclosed to the effect that the method has means to form a superposed portion by making the sheet feed per each of the main scans smaller than the width of a main scan so that the two adjacent main scans are superposed, and means to arrange the two main scans so as not to allow the printed dots in the aforesaid superposed portion to be superposed. In this laid-open application, a thinning mask is defined as xe2x80x9cprinted in cross wise in an odd number stage and an even number stage per one arrayxe2x80x9d in some cases, but in some other cases, the odd number stage is printed by a first main scan, and the even number stage is printed by a second scan or the recording is executed at random per scan. Hence there are no complete limits set to the thinning mask and the width of the sheet feed.
Meanwhile, in the latter specification of the U.S. Pat. No. 4,967,203, the thinning mask which executes divided recordings is limited to the alternate pixel arrangement which is not adjacent in the vertical and horizontal directions such as disclosed to the effect that:
a) with a first path, the alternate pixel positions which are not adjacent in the horizonal and vertical directions are printed only for the upper half in a first band;
b) with a second path, a printing is executed for the pixels in the first band which are not printed in the first path, and the alternate pixels which are not adjacent horizontally and vertically in the lower half of the first band; and
c) with a third path, the pixels in the first band which are not printed by the first and second paths are printed, and at the same time, the first path is executed for a band which immediately follows.
In this specification, a recording method is disclosed as an additional arrangement that several pixels are formed together as a super pixel to make a tonal representation and a multicolor representation, and that the alternate thinning printing is executed per super pixel. It is then described to the effect that according to this method, once a system to materialize the above-mentioned method is incorporated either in a programmed software or a printer (firmware) such a program can be called by the color number of the combination designated for the super pixel. As a result, without making the computer programming unnecessarily complicated for the preparation of many colors, this printing quality can be achieved. Also, as an effect, the simplification of the programming for the multicolor representation is described. Further, It is described that each of the super pixels is arranged with a purpose that it is recognized as a single homogeneous color, making any blur of colors in the super pixel harmless.
Now, in the conventional printer structured to arrange the recording heads for a plurality of colors in the direction of recording scan, there are some cases that the above-mentioned unevenness is created together with the color variation or the like if a bidirectional recording is attempted in order to enhance the recording speed without using the above-mentioned divided recording method. The reason will be described hereunder.
FIG. 6 is a cross-sectional view showing the state that the recording ink currently in use in general impacts on a recording medium (paper). Here, it is represented that ink (dots) of two different colors are absorbed (recorded) in the positions almost adjacent to each other with a time differential. Attention should be given to the fact that in the part where two dots are superposed, the dot which is impacted later than the dot which is recorded earlier tends to sink more in the depth direction of the sheet. This is because the coupling of the recording medium and the coloring matter of the dye in the discharged ink is made only at the stage where they are coupled physically and chemically, and also, because unless there is a great difference in the coupling force depending on the kinds of coloring matter, priority is given to the coupling of the recording medium and the coloring matter of the ink discharged earlier, and this coloring matter remains more on the surface of they recording medium, thus making it difficult for the coloring matter of the ink discharged later to couple with the recording medium on its surface. Conceivably, therefore, this coloring matter tends to sink in the depth direction of the recording medium in order to couple it.
In this case, even when two kinds of ink are recorded on the same impact point, the color priority becomes different depending on the order in which these two kinds of ink are impacted. Consequently, two different colors can appear by the way of order in which the imapacts are given because of the visual sensation of human eyes. For example, if a green (cyan+yellow) image should be formed in a given area, and ink is impacted on each of the pixels in order of cyan and yellow, the cyan which is absorbed earlier becomes the priority color, representing a green image having more cyanic coloring. On the contrary, if each ink is impacted in order of yellow and cyan, it is possible to obtain a green image having more yellowish coloring.
Here, taking a bidirectional recording into account, the order of impacting ink on the forward path and the order of impacting ink on the backward path are reversed because, as shown in FIG. 1, each of the color recording heads is arranged in the direction of recording scan. Therefore, the coloring of dots recorded on the forward path differs from that of dots, recorded on the backward path. If the sheet is being fed for a portion equivalent to the length of the discharge port arrangement per recording scan which is usually executed in such a state as above, the tonality and density of two different kinds appear alternately per scanning line, thus presenting a conspicous color unevenness in a recorded image as a whole, hence degrading the quality of the recorded image eventually.
However, a drawback of this kind can be overcome by use of the divided recording method described earlier. In other words, by executing the divided recording, it becomes possible as described in conjunction with FIG. 5 to mix the coloring of the dots recorded on the forward path (FIGS. 5A and 5C) and the coloring of the dots recording on the backward path (FIG. 5B) almost by half a number each in a given area. As a result, the difference in the coloring condition on both dots is averaged as a whole, making it possible to obtain just the intermediate coloring equally in any of the recording areas.
The above-mentioned structure and effect regarding the coloring condition are disclosed in the specification of U.S. Pat. No. 4,748,453, for example. Here, although no limit is set to the amount of sheet feed, the description is made to indicate that there is an effect to prevent the color banding (color unevenness) from taking place by reversing the orders of impacting ink on pixels of mixed colors for the first and second scans (reciprocal recording) for the formation of a color image when the ink beading should be avoided on a recording medium, a transparent film, for example, in such a manner that the recordings are executed complementarily by the divided recording scans into the first and second order (or more) for the pixels which are positioned alternately in the horizontal and vertical directions in each of the recording areas. In this specification, since the main purpose is to prevent the beading from taking place between each of the pixels, the method is characterized in that the pixels themselves, which are recorded per scan, are not adjacent to each other in the horizontal and vertical directions. A divided recording method of a kind is called xe2x80x9cmultipath printingxe2x80x9d.
In the meantime, the applicant hereof has disclosed the following method in Japanese Patent Laid-Open Application No. 58-194541:
A plurality of recording element arrays are arranged in parallel, and when a main scan is executed for the dot matrix recording by reciprocating the recording element arrays in the direction orthogonal to the aforesaid recording element arrays, each line of the recording dot matrix, and the dot numbers which are smaller than the total dots to be recorded at least on either one of the respective lines are intermittently recorded on the forward path of the aforesaid main scan, and at the same time, in the backward path of the aforesaid main scan, each of the aforesaid lines and the remaining dots at least on one of the respective lines are intermittently recorded. Thus the recording method is characterized in that the orders of superposition in which the superposed recording dots are recorded by the aforesaid plurality of recording element arrays are arranged to differ from each other on the forward path and the backward path of the aforesaid main scan. In this laid-open application, too, there is no limit set to the amount of sheet feed such as to make it smaller than the length of the recording element arrays as in the case of the divided recording described earlier. According to the disclosure, the effect of this method is to prevent the recorded image from being degraded due to the tonal deviation (color unevenness) of the recorded image caused by the repeated recording (superposed recording) in color ink. In this laid-open application, the main objective is the prevention of this tonal deviation. Therefore, no particular restriction is given to the positions of the dots to be recorded by each scan, and in its embodiments, there are described in addition to the checkered patterns (cross and counter-cross patterns), the horizontal thinning in which the recording is made alternately only in the vertical direction, and the vertical thinning in which the recording is made alternately only in the horizontal direction.
Also, in Japanese Patent Laid-Open Application No. 55-113573, there is disclosed a structure in which a reciprocal recording is executed by use of a pattern in the double-cut form (cross and counter-cross patterns), although not limited to a color printer. In this laid-open application, an arrangement is made so that no adjacent dots are printed continuously, and then, before the printed dots are dried, the adjacent dots are printed in order to achieve its objective, that is, to prevent any deformed dots from being created. Therefore, in this laid-open application, the thinning mask is limited to the pattern in the double-cut form as in the specification of the above-mentioned U.S. Pat. No. 4,748,453.
Now, the above-mentioned three disclosed specifications are all aimed at preventing the color unevenness and beading from being created when a reciprocal recording is executed. Therefore, unlike the divided recording method disclosed herein, none of them provides a structure that xe2x80x9cthe amount of sheet feed between each of scans is made less than the length of the discharge port arrangementxe2x80x9d as one of the objectives to prevent the density unevenness from being created due to the variation of the discharge ports. Also, none of them discloses the case where two or more kinds of ink having different densities are used for recording.
As described above, when the divided recording is executed in the reciprocal recording, it is possible to distribute the two kinds of recording pixels having the opposite orders of impacting ink colors evenly in a recording area, thus making it possible to solve the color unevenness and eliminate, at the same time, the density unevenness caused by the variation of the discharge ports.
Nevertheless, the phenomenon that the dot fixation state differs by the order in which the ink is impacted not only results in the above-mentioned color unevenness, but also this phenomenon is equally applicable to the case where ink having different densities are impacted. In other words, if a dot is recorded with ink of a high density earlier, the density of this dot which is recorded earlier is given priority so that a clear image can be obtained with a high density. On the other hand, if ink of a high density is impacted subsequent to ink of a low density having been impacted, such ink is greatly permeated around the ink of a low density so that a smooth and even image can be obtained with a density which is not so high.
As described above, when the plural ink having different darkness and lightness are used for each of the plural kinds of ink in consideration of the graininess in the recorded imagea in executing a color recording by use of plural kinds of ink, there appears the dark and light unevenness due to the order in which the dark and light ink are superposed, in addition to the color unevenness due to the order in which each kind of ink is superposed; hence varying more the way in which the color unevenness and as the dark and light unevenness appear.
To describe this condition more precisely, in the ink jet recording apparatus shown in FIG. 1, the arrangement of the conventional recording heads Kk to Yu used for a color recording as described above is made in such a way as shown in FIG. 7. Therefore, the combination of the superposition of various kinds of ink including the dark and light ones, which is arrangeable by way of scanning in executing a color recording, becomes more varied as compared to the case where no dark and light ink are used.
As a result, even if the color unevenness and dark and light unevenness are to be averaged by use of the above-mentioned divided recording method, it does not work good enough in some cases. Also, as described later, the color unevenness and others cannot be completely eliminated depending on the permeated area of the ink impacted on each of the dots.
Now, FIG. 45 is a view showing another structure of the ink jet recording apparatus which records by use of the dark and light ink. FIG. 45 illustrates the structure of the printer unit when printing on the surface of a sheet by use of the above-mentioned multihead. Here, it is assumed that four recording heads for four colors are provided in the recording scan direction for color printing. In FIG. 45, a reference numeral 701 designates ink cartridges. These cartridges comprise the ink tanks containing four color inkxe2x80x94black, cyan, magenta, and yellowxe2x80x94each separately prepared in dark and light ink; and the recording heads 702.
FIG. 7 is a view showing the state of the discharge ports arranged on the recording heads observed in the direction z in FIG. 45. Here, the dark ink discharge port are arranged and the light ink discharge port array are arranged on the black head. Adjacent to it, the dark ink discharge port array and light ink discharge port are arranged on the cyan head. In this way, two arrays of ink discharge ports are arranged each for the four colors. In this respect, the head for each color including the dark and light discharge ports is represented as if arranged independently, but if only the arrangement of ink discharge ports itself is equal to the above-mentioned structure, the state of image formation is also the same even if all the discharge ports for each of the colors and densities are arranged on one and the same head.
Now, reverting to FIG. 45, a reference numeral 703 designates a feed roller which rotates in the direction indicated by an arrow while pressing a printing sheet 707 in cooperation with an auxiliary roller 704 to feed a printing sheet 707 in the direction indicated by an arrow y at all times; 705, a supply roller which supplies the printing sheet, and at the same time, serves to press the printing sheet 707 in the same manner as the rollers 703 and 704; 706, a carriage which supports the four ink cartridges, and at the same time, enables them to travel when printing. The carriage is on standby in the home position h indicated by dotted lines in FIG. 45 when no operation is executed for printing or when a recovery operation is executed for the multihead.
Before starting a printing, the carriage 706 is in the home position shown in FIG. 45. With a printing start command, the recording is executed for an area of a width D on the sheet by use of the n number of multinozzles on the multihead 702 while traveling in the direction x. This recording is executed in such a manner that in accordance with the timing read by an encoder, the aforesaid heat generating elements are driven on the basis of recording signals to discharge ink droplets on a recording material in order of dark black, light black, dark cyan, light cyan, dark magenta, light magenta, dark yellow, and light yellow, thus allowing them to adhere to the recording material for the formation of images. When the printing of data is completed to the end portion of the surface of the sheet, the carriage returns to the home position originally set when the printing is started, and then, the printing is again started in the direction x (forward scan direction) or, if the printing is reciprocal, it is executed while the carriage travels in the direction xe2x88x92x (backward scan direction). During the period from the completion of the first printing to the start of the second printing, the feed roller 703 rotates in the direction indicated by an arrow to convey the sheet in the direction y for a portion equivalent to the width D. In this way, a printing and a sheet feed for the area equivalent to the multihead width D are repeated by means of the carriage and scan to complete the printing on one surface of the recording sheet.
With the multipath printing method or divided recording method set forth above, which is applicable to a bidirectional printing in this ink jet recording apparatus, it is possible to anticipate excellent effects in recording by use of several kinds of ink each having different densities in a color recording or in a monochrome printing using only black ink.
However, when a structure should be arranged so that a total of eight kinds of inkxe2x80x94yellow, magenta, cyan, and black, each prepared in dark and light inkxe2x80x94may be recorded simultaneously, it is not good enough if the division is provided only for one reciprocal scan because the time is often too short for ink to be dried sufficiently.
In addition to it, if the amount of ink impacted per dot becomes great, the ink is often permeated into the area of the other pixels. For example, as shown in FIG. 48, even in a state that a recording is made only for a 50% of the total area, almost all the area is covered eventually. If such a condition is brought about, the ink recorded by the scan in the opposite direction almost sinks into the lower side of the surface of the sheet due to the principle described in conjunction with FIG. 6. Consequently, on the surface of the sheet, the resultant image tends to present a biased tonality.
Also, if the divided recording method is being used, the area recorded by the backward scan subsequent to the earlier recording by the forward scan, and the area recorded by the forward scan subsequent to the earlier recording by the backward scan appear alternately by half a pitch of the recording width of the head; hence inevitably presenting a conspicuous color unevenness in the sheet feeding direction.
Further, in a case of a monochrome printing, although no color unevenness such as above appears, there often encountered the difference in the way of ink permeation into the surface of the sheet when using two kinds of ink each having different density. In other words, even in a monochromic color, there is a possibility that density unevenness appears in the sheet feeding direction depending on the order of impacting each of the two kinds of ink.
Conceivablly, therefore, the number of divisions is increased to provide a method in which a printing is executed by two-reciprocal scans or four-reciprocal scans, but in this case, the problem is that the required recording time becomes longer still; hence canceling the favorable effects-of the bidirectional printing.
The present invention is designed to solve the problems encountered in recording by use of a plurality of ink each having different densities as described above. It is an object of the invention to provide a recording head which contributes to miniaturizing the apparatus, and suppresses the unevennesses in a recorded image; and an ink jet recording apparatus.
Also, the present invention is designed in consideration of the foregoing subject, and is aimed at providing an ink jet recording apparatus and an ink jet recording method capable of obtaining excellent images without any density unevenness.
In order to solve the above-mentioned problems, an ink jet recording apparatus according to the present invention has a recording head provided integrally with a plurality of recording units having a plurality of discharge port arrays integrally arranged in the direction orthogonal to the direction of main scan for discharging each of different colored inks. The aforesaid plural recording units are arranged in the aforesaid direction of main scan, and discharge ink each having different densities at the same time.
Also, an ink jet recording apparatus according to the present invention has a recording head provided integrally with a plurality of discharge port arrays for discharging inks having different densities in the direction which differs from the aforesaid direction of main scan. Further, the aforesaid recording head is integrally provided with a plurality of recording units having a plurality of discharge port arrays arranged in the direction almost orthogonal to the aforesaid direction of main scan for discharging inks having different densities.
Also, an ink jet recording apparatus according to the present invention has a recording head provided with the discharge port array having a plurality of discharge ports arranged in the direction different from the aforesaid direction of main scan for discharging inks, wherein a plurality of discharge port arrays, which are arranged in the direction different from said direction of main scan for discharging ink each having different densities, are arranged in the aforesaid direction of main scan per color of the aforesaid ink, and then, all the pixels in a recordable area by a one-main scan of the recording head are thinned in accordance with a plurality of thinning arrangement patterns which are in a complementary relationship with each other. The thinned image is recording by plural numbers of main scans of the aforesaid recording head, and plural numbers of correlative movements of the aforesaid recording head and the recording medium in the direction different from the aforesaid scan.
Also, an ink jet recording apparatus according to the present invention has a recording head provided with the discharging ports having a plurality of discharge ports arranged in the direction different from the aforesaid direction of main scan for discharging inks, wherein a plurality of discharge port arrays, which are arranged in the direction different from the aforesaid direction of main scan for discharging ink each having different colors, are arranged in the aforesaid direction of main scan per density of the aforesaid ink, and then, all the pixels in a recordable area by a one-time main scan of the aforesaid recording head are thinned in accordance with a plurality of thinning arrangement patterns which are in a complementary relationship with each other. The thinned image is recorded by the plural numbers of the main scans of the aforesaid recording head, and the plural numbers of the correlative movements of the aforesaid recording head and the aforesaid recording medium in the direction different from the aforesaid main scan.
Also, a recording head according to the present invention is provided with a plurality of discharge port arrays having a plurality of discharge ports arranged in a given direction, and is characterized in that the aforesaid discharge port arrays are arranged with a plurality of discharge port groups for discharging inks each having different densities.
Also, a recording head according to the present invention is characterized in that a plurality of discharge ports are arranged in a given direction, and each of them is provided with a plurality of discharge port arrays having a plurality of discharge port groups for discharging inks each having different colors, and that the aforesaid plural discharge port arrays discharge inks each having different densities.
Also, an ink jet recording apparatus according to the present invention uses a recording head capable of discharging a plurality of inks each having different densities, and forms images by discharging ink from the aforesaid recording head to a recording medium while enabling the aforesaid head to scan the recording medium correlatively, and is characterized in that there is provided means for controlling ink discharges to form an image by discharging ink having a desired density, which is selected from among the aforesaid plural inks each having different densities, in a first scan of the aforesaid recording head, and then, in a second scan subsequent to the aforesaid first scan, to form the image in the image area formed by use of the ink of the aforesaid desired density by discharging the ink which has the density different from the aforesaid desired density, which is selected from among the aforesaid inks each having different densities.
Also, an ink jet recording apparatus according to the present invention uses a recording head capable of discharging a plurality of inks each having different densities, and forms images by discharging ink from the aforesaid recording head to a recording medium, and is characterized in that there are provided reciprocal scanning means to enable the aforesaid recording head to reciprocally scan a recording medium correlatively; recording head driving means to drive the aforesaid recording head for the formation of images during the reciprocal detection by the aforesaid reciprocal scanning means; and means for controlling ink discharge to form an image by discharging ink having a desired density, which is selected from among the aforesaid plural inks each having different densities, in a first reciprocal scan by the aforesaid reciprocal scanning means, and then, in a second reciprocal scan subsequent to the aforesaid first reciprocal scan, to form the image by discharging the ink which has the density different from the aforesaid desired density.
Also, an ink jet recording method according to the present invention, which uses a recording head capable of discharging a plurality of inks each having different densities, and forms images while enabling the aforesaid recording head to reciprocally scan a recording medium correlatively, comprises the following steps of:
forming an image by discharging ink having a desired density, which is selected from among the aforesaid plural inks each having different densities, in one of scans executed by the aforesaid reciprocal scanning; and
forming the image by discharging the ink having the different density from the aforesaid desired density, which is selected from among the aforesaid plural inks each having different densities, in the image area formed by use of the ink having the aforesaid desired density during the other scan executed by the aforesaid reciprocal scanning subsequent to the aforesaid one scan of the reciprocal scanning.
Also, an ink jet recording method according to the present invention, which uses a recording head capable of discharging a plurality of inks each having different densities, and forms images while enabling the aforesaid recording head to reciprocally scan a recording medium correlatively, comprises the following steps of:
forming an image by discharging ink having a desired density, which is selected from among the aforesaid plural inks each having different densities, in a first reciprocal scan; and
forming the image by discharging the ink having the different density from the aforesaid desired density, which is selected from among the aforesaid plural inks each having-different densities, in the image area formed by use of the ink having the aforesaid desired density during a second reciprocal scan subsequent to the aforesaid first reciprocal scan in the image area formed by use of the ink having the aforesaid desired density.